Cellular radiotelephone cells typically consist of a number of transmitters that transmit, in either omnidirectional or directional antenna patterns, from the cell. The highest capacity cells use directional antennas, dividing the cell into sectors. A major metropolitan area can consist of a large number of these cells. The cells are linked to the land telephone line allowing mobile radiotelephone users to access the land telephone lines and vice versa.
Using the cellular radiotelephone system, a mobile radiotelephone user can travel across a metropolitan area while keeping in contact with the land telephone lines. As a mobile user travels through an area, he may travel through more than one sector of a cell or, depending on the distance traveled, more than one cell. The cellular system takes care of handing off the user's call to another sector or cell.
The mobility of the user means that the sectors within a cell could have widely varying demand at any given time. This variability could cause some sectors to become overloaded while other sectors may have excess capacity. Presently, when a sector has more users than it can handle, the users trying to communicate in that sector are either shifted to another sector or they must wait for a frequency to become free.
Cellular base station receivers are diversity receivers which require 2 antenna inputs. In sector receive configurations, the 2 receiver inputs come from one even and one odd numbered sector that are adjacent. In order to route these 2 inputs from the odd or even antenna to the receiver, a configuration of passive splitters and matrix switches is used. The passive splitter splits the signal from the antenna into multiple signals to be handled by different receivers. The switch matrix switches the signals to the appropriate receivers. This configuration does not allow receivers to handle signals from any sector in the cell. Each receiver can only receive from the odd or even sector matrix to which it is assigned.
Each sector of a cell typically has a single antenna for transmitting. In order to transmit on multiple frequencies in that sector, therefore, multiple transmitters must be combined on that single antenna. FIG. 1 illustrates the present method of combining transmitters onto an antenna. The transmitters (A) produce a signal that is amplified (B) and passed through a combiner (C). The combiner (C) merges the signals allowing a number of transmitters (A) to transmit on one antenna (E).
The combiner (C) contains resonant cavities which each allow only one frequency at which the cavity is tuned to pass to the antenna (E). The cavities are manually tuned to a certain frequency which can only be changed by manually retuning the cavity. Therefore, only a limited number of fixed tuned frequencies can be transmitted from present sector cell configurations.
Because mobile traffic is not distributed evenly, it is continuously changing in number and location, and present transmitter hardware is limited to a fixed number of frequencies within a sector, there exists a need to move underutilized transmitters and/or frequencies from sector to sector with varying traffic demands.